“The safest general characterization of the European philosophical tradition”, wrote Alfred North Whitehead in Process and Reality, “is that it consists of a series of footnotes to Plato.”  If he is even partially or qualifiedly correct, we would be remiss not to make ourselves familiar with Plato’s writings.
Plato (420’s–348/347 B.C.) did not write treatises, but dialogues (letters aside). Plato himself does not directly show up in these dialogues — similar to how Shakespeare does not directly appear in his plays. Likewise, just as locating Shakespeare’s voice among the voices of his characters can be quite tricky, so too locating Plato’s voice is not always a simple affair.
Plato’s dialogues are customarily divided into three periods — his early, middle, and later dialogues. His early dialogues are understood to focus on Socrates as a moral philosopher, where ethical concerns predominate in response to what can rightly be called the moral relativism and skepticism of the Sophists. (To oversimplify: the Sophists were a phenomenon, rather than an organized group, like a church or a guild: the Sophists were rhetoricians, public speakers who would teach the art of persuasion-through-speech to clients willing to pay them. In Athens, where laws were passed –or vetoed– by speaking in the public assembly, this skill was a veritable means to power.) Plato’s middle dialogues also feature Socrates as the protagonist, although these middle dialogues are where we get the first flowering of Plato’s more mature thought, with a more robust and developed metaphysics and epistemology on display, among other things (the well-known Republic is among these middle dialogues). His later dialogues are not our concern here.
Plato’s dialogue the Phaedo is usually classed as the final of a trilogy of dialogues dealing with the trial and death of Socrates: the Euthyphro, the Apology, and then our dialogue, the Phaedo. The Euthyphro and the Apology are usually dated to Plato’s early period, but the Phaedo is dated to his middle period, and the more mature metaphysical concerns of his middle period are well on display in this dialogue.
There is one section of the Phaedo where Plato has Socrates recount Socrates’ own philosophical path, his own intellectual biography. It is fascinating, and some of us might be tempted to read it either as an intellectual biography either of Socrates or Plato. We must be careful.
In general, the Phaedo is better read as a philosophical memoir than as a biographical record. Even the famous passage in which Socrates rehearses the story of his intellectual development (96a–100a) [our excerpt, link below] is artfully contrived to serve a philosophical purpose, and may have little or no foundation in fact. 
There it is: you’ve been warned.